We extracted 947 sanitary registrations from the COFEPRIS public database spanning 79 rheumatology-relevant drugs in Mexico — biologics, biosimilars, JAK inhibitors, conventional DMARDs, NSAIDs, corticosteroids, immunosuppressants, bone agents, and crosslink specialties.

Key finding: biosimilar indication coverage is NOT uniform. For adalimumab alone, approved indications range from 4 (YUFLYMA) to 15+ (HUMIRA innovator). This creates a natural experiment — regulatory indication gaps as informative priors for Markov chain transition matrices.

Registration distribution: 63% generic, 17% reference, 3% biosimilar, 3% novel molecule, <1% orphan.

The Markov model uses 3-month cycles (rheumatology follow-up intervals) with states: Remission → Low Disease Activity → Moderate → Severe → Biologic Switch → Treatment Failure.

Preliminary: For RA, innovator vs biosimilar transition probabilities are indistinguishable. But for extrapolated indications (uveitis, hidradenitis), parametric uncertainty increases 8-15% in cost-effectiveness estimates.

This framework is directly applicable to IMSS formulary decisions where biosimilar adoption is accelerating but indication-specific evidence gaps persist.

Full dataset (947 registrations, JSON) and COFEPRIS scraper source code available.

Authors: Dr. Erick Adrián Zamora Tehozol (CryptoReuMd.eth) & DNAI